Girl next door

Ionic

There's no getting around technical stuff here, but I'll keep it as simple as possible. What ionic technology does is generating negative ions to counter the positive ions we see in dry or damaged hair. It works in conjunction with materials and coatings such as Tourmaline Ionic or Ceramic Ionic.
Infrared

The wavelength of infrared technology is longer than most conventional heat styling methods, allowing the heat to penetrate directly into the hair shaft. This means less time for styling, and less heat exposure.
Nano

I searched and searched for both ionic and nano technology to explain the difference, but there's a lot of hype and it all comes down to the same thing. They're just fancy marketing terms for saying the negative ions protect your hair.
Silver

This isn't so much about heat distribution or hair protection, but more about hygiene. Silver is used to eliminate the bacteria on your straightening iron, making the plates free from germs and microbes.

If I have Thick, Curly Hair

Aside from personal preference and styling wishes, these are the general guidelines:
Short Hair - 1 to 1.5 Inch
Shoulder Length - 1 to 2 Inch
Long Hair - 1.5 to 2 Inch
If I have Normal, Wavy Hair

Aside from personal preference and styling wishes, these are the general guidelines:
Short Hair - 0.5 to 1.25 Inch
Shoulder Length - 1 to 1.5 Inch
Long Hair - 1.25 to 2 Inch
If I have Thin, Fine Hair

You're in luck, you can go any direction you want. Just remember that small plates give more styling flexibility, and wider plates means a quicker straighten, especially for longer hair.

Do straightening irons damage my hair?

Hair straighteners apply heat to your hair, and this weakens the protective hair cuticles. The severity and speed of the damage is very personal though and depends both on your hair and the way you use your flat iron. Don't overdo it, and protect your hair from heat as much as you can.
Should I use heat protectants?

Basically we already answered this with the previous question: Yes, it's better for your hair to use heat protection products. Use your preferred spray or oil, and give your hair a regular deep condition to keep it hydrated.
Is it better to use lower temperatures?

The optimal temperature is around 365^oF but depends on the structure and thickness of your hair, as well as the styling you're after. Lowering it for the sake of damage control is often counter-effective, because you'd have to do more passes through your hair.
Should I go for changeable plates?

Well, if you sometimes use a waver or crimping iron then you might as well buy an all-in-one straightening iron. Personally I believe more in products that are made for a specific task, but you do save yourself space and money.